ppl are always missing the things that Shizuko already said XD, before she was enslaved she already said that all of the girls are living a loveless marriage, which is common after the 20s+ in this world.
It's not like NTR, it's mostly.... at the best and luckiest you see your wife as your friend and if someone is willing to actually love her, in this world they see "oh well sure why not, I might get a younger girl or slave then, take care of her" thats how detached from woman 20+ they are XD.
Didnt the MC said already in the first Chapter that because of all this crap he see everyone in this world as a bunch of Pedos? XD
Think like your friend showing up at your house "oh dude, you know this old TV you are not using anymore? Can I have it? I promisse I will take care"
This is how bad they are treated XD